Scientists have discovered an ancient fossil of the earliest animal on geological record. Called “Dickinsoni”, this strange oval creature had rib-like segments running along its body that lived on Earth 558 million years ago.

According to a new paperpublished last week in Science, in which researchers argue an iconic fossil from this time period is the oldest known animal that would have been visible without the help of a microscope.

The scientists discovered molecules of fat in an ancient fossil of an oval-shaped creature called Dickinsonia, growing up to 1.4 meters in length.

The animal with rib-like segments running along its body was part of the Ediacara Biota that lived on Earth 20 million years prior to the so-called “Cambrian explosion”.

Dickinsoniid ontogeny.The Cambrian explosion was the period of time in history when complex animals and other macroscopic organisms evolved rapidly and began to dominate the Earth and the hence the fossil record left behind.

The research team discovered the fossil in a remote area near the White Sea in the northwest of Russia that the tissue still contained molecules of cholesterol, a type of fat that is the hallmark of animal life.

Being able to finally study the fat molecules from the ancient organisms was a “game changer” according to Associate Professor and ANU senior researcher Jochen Brocks.

The fossil fat molecules confirmed Dickinsonia to be the oldest known animal fossil. It holds the key between the old world dominated by bacteria and the world of large animals that emerged 540 million years ago during the “Cambrian explosion.”